The major objective is the specification of the qualitative and quantitative facts of noise-induced hearing loss, particularly asymptotic threshold shifts in human observers. A second objective is to specify the audiometric correlates of asymptotic threshold shifts, particularly temporal integration, psychophysical tuning curves, and physiological response assumed to arise from the brain stem and auditory cortex. Groups of human subjects are exposed to noise for durations as long as 48 hours. Measurements are made before, and after the noise exposure as well as during quiet periods interspersed within an exposure. The exposures are selected in order to evaluate the Equivalent Power Model and/or to noise produce a given temporary hearing loss which can be evaluated with current psychophysical and physiological tests of hearing. Results are expected to have a significant impact on the topic of noise-induced hearing loss and in establishing criteria for the development of the acoustic environment. In addition, many of the methods developed here have immediate application to the diagnosis and treatment of hearing loss and deafness, particularly in infants and young children.